This disclosure relates generally to air handling systems for buildings, more particularly to energy recovery ventilation systems, and specifically to a temperature and/or enthalpy control for an energy recovery wheel.
The present disclosure is directed to systems and methods which control energy recovery ventilation (ERV) systems of buildings. ERV systems may be used to recover energy and lower utility expenses. Energy recovery wheels rotate between the incoming outdoor air and the exhaust air. As the wheel rotates, it transfers a percentage of the heat and moisture differential from one airstream to the other. The outdoor air is pre-conditioned reducing the capacity and energy needed from the mechanical HVAC system. According to guidelines, building environments require a specific amount of fresh air to dilute contaminates in the space and provide ventilation for high concentrations of people. The required amount of fresh air may provide dilution of contaminates, to minimize the possibility of “sick building syndrome.” Increasing the outside air intake lowers the carbon dioxide levels in the building, and may help keep the occupants alert and healthier. ERVs may also reduce indoor odors with fresh outside air that is brought into the building as stale air may be exhausted out of the building.
When fresh air is brought into a building, conditioned air from the inside may be exhausted to the outside to equalize pressure. The energy of the conditioned exhaust air leaving the building may be used to pre-condition outside fresh air in the summer and winter. When conditions are suitable for free cooling in the spring and/or fall, the energy recovery ventilator enters an economizer sequence.
An energy recovery ventilation wheel (wheel) may be used within an ERV. The rotating wheel heat exchanger may be composed of a rotating cylinder filled with an air permeable material resulting in a large surface area. The surface area is the medium for the sensible and/or enthalpy energy transfer. As the wheel rotates between the ventilation and exhaust air streams it picks up heat energy and releases it into the colder air stream. The driving force behind the exchange is the difference in temperatures between the opposing air streams. Typical media used consists of polymer, aluminum, and synthetic fiber.
The enthalpy exchange is accomplished through the use of desiccants. Desiccants transfer moisture through the process of adsorption which is predominately driven by the difference in the partial pressure of vapor within the opposing air-streams. Typical desiccants consist of silica gel, and molecular sieves.
One disadvantage of using a wheel is moisture build up in and on the wheel. In one embodiment, a sequence of operation is undertaken, with inputs from the outside enthalpy and/or temperature to control the operation of the sequence.
Representative of the art is U.S. Pat. No. 6,205,797 which discloses an air conditioning system and operation method, having dehumidification ability and flexibly adaptable for processing a variety of conditioning loads, and also energy conserving. The invention comprises a desiccant for adsorbing moisture from process air, and a heat pump, including a compressor, that operates by using process air as a low-temperature heat source and regeneration air as a high-temperature heat source so as to supply heat to regeneration air for regenerating the desiccant. Processes of heat transfer in a sensible heat exchanger are made adjustable, for exchanging heat between post-desiccant process air that has not flowed into the low temperature heat source heat exchanger and pre-desiccant regeneration air that has not yet regenerated the desiccant.